The purpose of this study is to test whether Fondaparinux is effective and safe to prevent thromboembolic events (like for example strokes) and bleeding events in patients who undergo a normalisation of their heart rhythm disturbance. Fondaparinux will be compared with Heparin and tablets containing Vitamin-K-Antagonists (Phenprocoumon, Fluindione, or Warfarin).

Number of Participants With at Least One Event of Cerebral Neurologic Event, Systemic Thromboembolism, Death From Any Cause, and/or Major Bleeding Until the End of Treatment (EOT) Plus 4 Days [ Time Frame: Baseline (Day 1) until Day 64 (4 days after the EOT [i.e., last administration of study drug]) for CP participants; Baseline until Day 36 (4 days after the EOT) for CN participants ] [ Designated as safety issue: No ]

Cerebral neurologic events are defined as any new neurologic disorders caused by cerebrovascular embolization, e.g., Transient Ischemic Attack (TIA), cerebral infarction. The cerebrovascular origin of the event has to be confirmed by objective procedures. Systemic thromboembolism comprises any arterial thromboembolic event (e.g., peripheral vascular embolism, mesenteric infarct, or myocardial infarction). All cerebral neurologic events were adjudicated by a Central Adjudication Committee (CAC), members of which were unaware of the participants' treatment assignment.

Secondary Outcome Measures:

Number of Thrombus-negative and Thrombus-positive Participants (Par.) With at Least One Cerebral Neurologic Event [ Time Frame: Baseline (Day 1) until Day 64 (4 days after the EOT [i.e., last administration of study drug]) for CP participants; Baseline until Day 36 (4 days after the EOT) for CN participants; and from Baseline until the follow-up visit (FU) (Day 90+/-7) ] [ Designated as safety issue: No ]

Cerebral neurologic events are defined as any new neurologic disorders caused by cerebrovascular embolisation, e.g., TIA, cerebral infarction. All cerebral neurologic events were adjudicated by a CAC, members of which were unaware of the participants' treatment assignment.The cerebrovascular origin of the event was confirmed by objective procedures. A thrombus or blood clot is the final product of the blood coagulation step in hemostasis. It is achieved via the aggregation of platelets that form a platelet plug, and the activation of the humoral coagulation system (i.e., clotting factors).

Number of Thrombus-negative and Thrombus-positive Participants With at Least One Systemic Thromboembolism [ Time Frame: Baseline (Day 1) until Day 64 (4 days after the EOT [i.e., last administration of study drug]) for CP participants; Baseline until Day 36 (4 days after the EOT) for CN participants; and from Baseline until the follow-up visit (FU) (Day 90+/-7) ] [ Designated as safety issue: No ]

Systemic thromboembolism comprises any arterial thromboembolic event (e.g., peripheral vascular embolism, mesenteric infarct, or myocardial infarction). All systemic thromboembolic events were adjudicated by a CAC, the members of which were unaware of the participants' treatment assignment. A thrombus or blood clot is the final product of the blood coagulation step in hemostasis. It is achieved via the aggregation of platelets that form a platelet plug, and the activation of the humoral coagulation system (i.e., clotting factors).

Number of Thrombus-negative and Thrombus-positive Participants Who Died From Any Cause [ Time Frame: Baseline (Day 1) until Day 64 (4 days after the EOT [i.e., last administration of study drug]) for CP participants; Baseline until Day 36 (4 days after the EOT) for CN participants; and from Baseline until the follow-up visit (FU) (Day 90+/-7) ] [ Designated as safety issue: No ]

The cause of death was classified as due to a thromboembolic event (like cerebral infarction), bleeding, or other established diagnosis, or as unexplained. All deaths were adjudicated by an independent CAC, the members of which were unaware of the participants' treatment assignment. A thrombus or blood clot is the final product of the blood coagulation step in hemostasis. It is achieved via the aggregation of platelets that form a platelet plug, and the activation of the humoral coagulation system (i.e., clotting factors).

Number of Thrombus-negative and Thrombus-positive Participants With at Least One Major Bleeding Event [ Time Frame: Baseline (Day 1) until Day 64 (4 days after the EOT [i.e., last administration of study drug]) for CP participants; Baseline until Day 36 (4 days after the EOT) for CN participants; and from Baseline until the follow-up visit (FU) (Day 90+/-7) ] [ Designated as safety issue: No ]

Major bleeding: fatal, and/or symptomatic in a critical area/ organ, causes a fall in hemoglobin of >=3 grams/deciliter compared with the pre-randomization level, or leads to the transfusion of >=2 units of whole blood/red blood cells. All bleeding events were adjudicated by a CAC, the members of which were unaware of the participants' treatment assignment. A thrombus/ blood clot is the final product of the blood coagulation step in hemostasis. It is achieved via the aggregation of platelets, and the activation of the humoral coagulation system (i.e., clotting factors).

Number of Thrombus-negative and Thrombus-positive Participants With at Least One Minor Bleeding Event [ Time Frame: Baseline (Day 1) until Day 64 (4 days after the EOT [i.e., last administration of study drug]) for CP participants; Baseline until Day 36 (4 days after the EOT) for CN participants; and from Baseline until the follow-up visit (FU) (Day 90+/-7) ] [ Designated as safety issue: No ]

Minor bleeding is defined as clinically overt bleeding events that do not meet the criteria for major or clinically relevant non-major bleeding. All episodes of bleeding were adjudicated by an independent CAC, the members of which were unaware of the participants' treatment assignment.

Number of Participants With Primary Successful Electrical Cardioversion (CV) in Sinus Rhythm [ Time Frame: Day 1 until Day 3 ] [ Designated as safety issue: No ]

CV may be performed electively to restore sinus rhythm in patients with persistent AF. The primary successful electric CV was assessed by a 12- lead electrocardiogram (ECG) directly after the CV. Results of the last cardioversion were used in cases for which more than one CV was performed.

Number of Participants With a Thrombus in the Left Atrium (LA) or in the Left Atrial Appendage (LAA) at the Time of the Second TEE [ Time Frame: At second TEE (at Day 28+/-4) ] [ Designated as safety issue: No ]

Atrial fibrillation (AF) causes stagnant blood in the LA or LAA and can lead to a thromboembolism. Stasis in the LAA represents the principal mechanism of thrombus formation in AF.

Number of Thrombus-negative and Thrombus-positive Participants With Conversion to Sinus Rhythm [ Time Frame: Baseline (Day 1) until Day 64 (4 days after the EOT [i.e., last administration of study drug]) for CP participants; Baseline until Day 36 (4 days after the EOT) for CN participants; and from Day 64 until the follow-up visit (FU) (Day 90+/-7) ] [ Designated as safety issue: No ]

Sinus rhythm is the normal beating of the heart, as measured by an ECG. Normal sinus rhythm not only indicates that the rhythm is normally generated by the sinus node and is traveling in a normal fashion in the heart, but it also indicates that the heart rate (the rate at which the sinus node is generating impulses) is within normal limits.

Number of Participants Who Were Re-hospitalized [ Time Frame: Baseline (Day 1) until Day 64 (4 days after the EOT [i.e., last administration of study drug]) for CP participants; Baseline until Day 36 (4 days after the EOT) for CN participants; and from Baseline until the follow-up visit (FU) (Day 90+/-7) ] [ Designated as safety issue: No ]

Hospitalization signifies that the participant has been detained (usually involving at least an overnight stay) at the hospital or emergency ward for observation and/or treatment that would not have been appropriate in the physician's office or out-patient setting. Re-hospitalization refers to an event of hospitalization after discharge for the initial hospitilization for the cardioversion.

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Please refer to this study by its ClinicalTrials.gov identifier: NCT00911300